Geoscience Reference
In-Depth Information
streams and rivers of birth before heading out to sea, but the estuary may serve as an important way station for
feeding.
In the Gulf of St. Lawrence, anadromous species also follow a predictable spawning regimen. Gaspereau (or
alewives) make their upriver spawning runs in May and June, and salmon surge into most rivers bordering the
gulf in October and November. Some gulf rivers, like the Restigouche, Miramichi, and Margaree, also have a
spring run of spawning salmon that enter the river in June. The Miramichi also has a spawning population of
striped bass, which enter the river in late May to the middle of June. Finally, smelt migrate into estuaries and
bays in late fall and overwinter there until March.
A series of barrier beaches and islands have developed along the shoreline in the southern Gulf of St.
Lawrence. Because of the semi-enclosed nature of the gulf, the shoreline is relatively protected from the wave
action of the open Atlantic. There is less wear and tear on the shoreline because the southern gulf is also ice-
covered for at least three months of the year, beginning in late December. Furthermore, the prevailing winds
are westerly, and so the fetch of the wind is short along most of the shoreline, with the exception of the Mag-
dalen Islands, which are more exposed. These features differentiate the barrier island and dune systems of the
gulf from those systems that prevail along the eastern seaboard, from Cape Cod to Florida, which is fully ex-
posed to the open Atlantic. Otherwise, the systems have much in common.
The centerpiece of this dramatic coastline is the Prince Edward Island National Park, a narrow coastal strip
of 32 kilometers (20 miles) protecting a diversity of coastal habitats: in turn, beaches, sand dunes, brackish
ponds (or barachois), and maritime coastal forests, as one progresses from the tide line toward the land. These
seemingly different habitats are produced by a single process, which begins with the erosion of the soft sand-
stone sediments that make up the island's red coastal cliffs and soils. Wave action from the gulf is constantly
eating away at this fragile bedrock, breaking it down into sand particles. This sets in motion a dynamic process
whereby the sand is first transported offshore and then deposited at the surfline to form the barrier islands,
beaches, and dunes that string along the Island's North Shore.
Wind and water constantly reshape this coastline. The water is very shallow, only 16 meters (52 feet) deep
as far offshore as 16 kilometers (10 miles), and for this reason, the wind-driven waves easily re-suspend the
sand and silt and carry it toward the shore, where it piles up above sea level to form offshore bars and sand-
spits. These barrier beaches sometimes form offshore islands such as Hog Island, at the mouth of Malpeque
Bay. However, storms, abetted by rising sea levels, have acted together to move much of the barrier island sys-
tem, depositing it as landfast barrier beaches. Once the sand is above the waterline, onshore winds whip up the
sand particles and carry them farther inland, the first step in the creation of a dune.
As a loose assemblage of sand particles, a dune is inherently unstable. It is the adaptations of sand-loving
marram grass that stabilizes the dune. While the leaves and stems act as sand catchers, the rhizomes branch out
to form a root system several meters in length, which anchors the dune, creating a relatively stable landform.
The foredunes are higher at their leading, windward edge and taper on the landward side, in the lee of the
wind, forming a crescent shape. The dunes run parallel to the shore and are subject to constant sculpting and
reshaping. Exposed to the forceful onshore winds, the face of the dune is bare sand, but the lee side supports
luxuriant growths of marram grass. Storm winds can cause “blow-outs,” however, undermining the marram
root system. And as the face of the foredune grows higher, the supply of sand on the lee side is diminished,
slowing the growth of the marram.
